1. Field of the Invention.
The present invention relates to a device for measuring a sound velocity in material by means of using a piezoelectric substrate, an interdigital arrangement of two comb-shaped electrodes formed on an upper end surface of the piezoelectric substrate, a counter electrode formed on a lower end surface of the piezoelectric substrate, a distance adjusting system, a reflector, and a signal analyzer.
2. Description of the Prior Art.
Ultrasonic techniques for measuring the sound velocity in a liquid are essential, of late years, in the field of physical acoustics, industry, physical chemistry, biophysics, medical science, and others. A thickness mode piezoelectric transducer with parallel plate-like electrodes is commonly used for this purpose. Separating a delayed electric signal from an input electric signal is necessary for such a conventional type of transducer, because the conventional type of transducer is used both as input- and output electrodes. Thus, such the conventional type of transducer has a difficulty in quick response measurement, and a complicated circuit-construction.
On the other hand, an interdigital transducer on the piezoelectric substrate operates at a liquid-solid boundary as a leaky wave transducer for bulk wave radiation into the liquid. The leaky SAW traveling on a sufficiently thick substrate compared with the wavelength has only one mode without velocity dispersion. Such the interdigital transducer for the leaky SAW has a difficulty in making the radiation angle vertical, so that has a difficulty in use and measurement accuracy.
An object of the present invention is to provide a device for measuring a sound velocity in material capable of making an interdigital transducer act as a thickness mode transducer.
Another object of the present invention is to provide a device for measuring a sound velocity in material operating with a quick response.
Another object of the present invention is to provide a device for measuring a sound velocity in material need not a circulator, and so on.
Another object of the present invention is to provide a device for measuring a sound velocity in material capable of making the radiation angle vertical.
Another object of the present invention is to provide a device for measuring a sound velocity in material capable of low electric power consumption.
Another object of the present invention is to provide a device for measuring a sound velocity in material capable of measuring the sound velocity in cellular tissue.
Another object of the present invention is to provide a device for measuring a sound velocity in material excellent in durability and manufacturing.
Another object of the present invention is to provide a device for measuring a sound velocity in material, which is not affected by a change in circumstances, for example, a change in temperature.
A still other object of the present invention is to provide a device for measuring a sound velocity in material easy in use and having a small size which is very light in weight and has a simple structure.
According to one aspect of the present invention there is provided a device for measuring a sound velocity in material comprising a piezoelectric substrate, first- and second comb-shaped electrodes formed on an upper end surface of the piezoelectric substrate, a counter electrode formed on a lower end surface of the piezoelectric substrate, a reflector parallel with the lower end surface of the piezoelectric substrate, a distance adjusting system, and a signal analyzer. The counter electrode is in contact with a surface-part of a material. The reflector is in contact with the opposite surface-part of the material. The distance adjusting system adjusts distances Zi (i=1, 2, . . . , n) between the surface-part and the opposite surface-part of the material in turn. The first- and second comb-shaped electrodes form an interdigital arrangement.
If input electric signals with a frequency f, respectively, are applied between the first comb-shaped electrode and the counter electrode in turn, longitudinal waves along the direction vertical to the lower end surface of the piezoelectric substrate are radiated into the material. The longitudinal waves are reflected at the reflector. Reflected longitudinal waves are detected between the second comb-shaped electrode and the counter electrode as delayed electric signals Di (i=1, 2, . . . , n) in accordance with the distances Zi. On the other hand, electrical coupled-signals from the input electric signals are also detected between the second comb-shaped electrode and the counter electrode. The electrical coupled-signals and the delayed electric signals Di interfere respectively with each other, so that respective interference signals Ri (i=1, 2, . . . , n) occur. Tracing a dependence of respective amplitudes of the interference signals Ri on the distances Zi provides a distance periodicity xcex94Z. Thus, a sound velocity V in the material is calculated from the product of twice the frequency f and the distance periodicity xcex94Z, that is, V=2fxcex94Z.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material, wherein the ratio of the interdigital periodicity of the interdigital arrangement to the thickness of the piezoelectric substrate is smaller than four times the ratio of the longitudinal wave velocity in the material to the longitudinal wave velocity in the piezoelectric substrate.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material, wherein increasing the number of electrode-finger pairs in the interdigital arrangement makes the directionality of the longitudinal waves sharper under a condition that the total amount of all the finger-areas of the first comb-shaped electrode is constant.
According to another aspect of the present invention there is provided a piezoelectric substrate made of a piezoelectric ceramic plate, the polarization axis thereof being parallel to the thickness direction thereof.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material, wherein the material is a liquid matter.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material, wherein the material is a cellular tissue.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material further comprising a polymer film, with which the lower end surface of the counter electrode is coated.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material further comprising a silicone rubber, with which the lower end surface of the counter electrode is coated.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material comprising a first piezoelectric substrate, a first interdigital arrangement of two comb-shaped electrodes formed on a lower end surface of the first piezoelectric substrate, a second piezoelectric substrate, a second interdigital arrangement of two comb-shaped electrodes formed on an upper end surface of the second piezoelectric substrate, a counter electrode cemented between the first- and second piezoelectric substrates, a reflector parallel with the lower end surface of the first piezoelectric substrate, a distance adjusting system, and a signal analyzer. A lower end surface of the first interdigital arrangement is in contact with a surface-part of a material. The reflector is in contact with the opposite surface-part of the material. The distance adjusting system adjusts distances Zi (i=1, 2, . . . , n) between the surface-part and the opposite surface-part of the material in turn.
If input electric signals with a frequency f, respectively, are applied between one of the two comb-shaped electrodes in the first interdigital arrangement and the counter electrode, longitudinal waves along the direction vertical to the lower end surface of the first piezoelectric substrate are radiated into the material. The longitudinal waves are reflected at the reflector. Reflected longitudinal waves are detected between one of the two comb-shaped electrodes in the second interdigital arrangement and the counter electrode as delayed electric signals Di (i=1, 2, . . . , n) in accordance with the distances Zi. On the other hand, electrical coupled-signals from the input electric signals are also detected between the one of the two comb-shaped electrodes in the second interdigital arrangement and the counter electrode. The electrical coupled-signals and the delayed electric signals Di interfere respectively with each other, so that respective interference signals Ri (i=1, 2, . . . , n) occur. Tracing a dependence of respective amplitudes of the interference signals Ri on the distances Zi provides a distance periodicity xcex94Z. Thus, a sound velocity V in the material is calculated from the product of twice the frequency f and the distance periodicity xcex94Z, that is, V=2fxcex94Z.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material, wherein the finger direction of the second interdigital arrangement is orthogonal to that of the first interdigital arrangement.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material, wherein the finger width in the one of the two comb-shaped electrodes in the first interdigital arrangement is wider than that in the other of the two comb-shaped electrodes in the first interdigital arrangement, and the finger width in the one of the two comb-shaped electrodes in the second interdigital arrangement is wider than that in the other of the two comb-shaped electrodes in the second interdigital arrangement.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material, wherein the ratio of the interdigital periodicity of the first interdigital arrangement to the thickness of the first piezoelectric substrate is smaller than four times the ratio of the longitudinal wave velocity in the material to the longitudinal wave velocity in the first piezoelectric substrate.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material, wherein increasing the number of electrode-finger pairs in the first interdigital arrangement makes the directionality of the longitudinal waves sharper under a condition that the total amount of all the finger-areas of the one of the two comb-shaped electrodes in the first interdigital arrangement is constant.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material comprising a first piezoelectric substrate, a first comb-shaped electrode formed on a lower end surface of the first piezoelectric substrate, a second piezoelectric substrate, a second comb-shaped electrode formed on an upper end surface of the second piezoelectric substrate, a counter electrode cemented between the first- and second piezoelectric substrates, a reflector parallel with the lower end surface of the first piezoelectric substrate, a distance adjusting system, and a signal analyzer. A lower end surface of the first comb-shaped electrode is in contact with a surface-part of a material. The reflector is in contact with the opposite surface-part of the material. The distance adjusting system adjusts distances Zi (i=1, 2, . . . , n) between the surface-part and the opposite surface-part of the material in turn.
If input electric signals with a frequency f, respectively, are applied between the first comb-shaped electrode and the counter electrode, longitudinal waves along the direction vertical to the lower end surface of the first piezoelectric substrate are radiated into the material. The longitudinal waves are reflected at the reflector. Reflected longitudinal waves are detected between the second comb-shaped electrode and the counter electrode as delayed electric signals Di (i=1, 2, . . . , n) in accordance with the distances Zi. On the other hand, electrical coupled-signals from the input electric signals are also detected between the second comb-shaped electrode and the counter electrode. The electrical coupled-signals and the delayed electric signals Di interfere respectively with each other, so that respective interference signals Ri (i=1, 2, . . . , n) occur. Tracing a dependence of respective amplitudes of the interference signals Ri on the distances Zi provides a distance periodicity xcex94Z. Thus, a sound velocity V in the material is calculated from the product of twice the frequency f and the distance periodicity xcex94Z, that is, V=2fxcex94Z.
According to another aspect of the present invention there is provided a device for measuring a sound velocity in material, wherein the finger direction of the second comb-shaped electrode is orthogonal to that of the first comb-shaped electrode.
According to other aspect of the present invention there is provided a device for measuring a sound velocity in material, wherein the ratio of the interdigital periodicity of the first comb-shaped electrode to the thickness of the first piezoelectric substrate is smaller than four times the ratio of the longitudinal wave velocity in the material to the longitudinal wave velocity in the first piezoelectric substrate.
According to a further aspect of the present invention there is provided a device for measuring a sound velocity in material, wherein increasing the number of electrode-finger pairs in the first comb-shaped electrode makes the directionality of the longitudinal waves sharper under a condition that the total amount of all the finger-areas of the first comb-shaped electrode is constant.